Optical signals used in high speed circuits and systems such as telecommunication typically are transmitted over long distance in fiber optic cables. However, on an integrated circuit these signals travel in interconnections called optical waveguides. Optical waveguides in integrated circuits are formed as cores surrounded by one or more cladding layers on a substrate for the purpose of transmitting selected modes of optical radiation. The index of refraction of the core is, for at least one polarization in at least one direction, greater than the index of refraction for materials adjacent to the waveguide core, typically called cladding. This difference in index of refraction keeps the light traveling within the optical waveguide due to total internal reflection.
High speed communication systems require optical components that are high speed with low absorption and scattering loss of the optical signal traveling in the optical waveguide. Optical waveguides in integrated circuits fall into two general categories, those using organic and those using inorganic glass core materials and cladding. Inorganic glass waveguides such as SiO.sub.2 have proven to be capable extremely low loss, while organic waveguides offer simplified fabrication and electro-optic capability but typically without the lower loss of inorganics.
Hybrid structures have been gaining interest in the optical arena because of the ability to utilize and combine processes and materials that are not completely compatible into a multi-functional device. Yamada et. al discloses a hybrid Mach-Zender interferometer circuit consisting of silica-waveguide directional couplers and a LiNbO.sub.3 drop in phase shifter chip in "An Application of a Silica-on-Terraced-Silicon Platform to Hybrid Mach-Zender Interferometer Circuits Consisting of Silica-Waveguides and LiNbO.sub.3 Phase-Shifters," IEEE Photonics Tech. Letters, Vol. 6 No. 7 July 1994. The device uses an integration platform consisting of a optical waveguide in a silicon substrate with a terraced region, an STS platform (Silica-on-Terraced -Silicon-Platform) to form an optical bench for the optoelectronic device composed of LiNbO.sub.3.